Fair Value Measurements and Derivative Instruments (Details 7) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Asset Derivatives
Asset Derivatives	$ 96,489	$ 201,130
Liability Derivatives
Liability Derivatives	85,119	84,344
Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	83,797	179,345
Liability Derivatives
Liability Derivatives	64,939	72,357
Designated as Hedging Instrument | Collars | Other Assets
Asset Derivatives
Asset Derivatives	8,974
Not Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	12,692	21,785
Liability Derivatives
Liability Derivatives	20,180	11,987
Interest rate swaps | Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	5,099	65,531
Interest rate swaps | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	55,471	11,369
Cross currency swaps | Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives		2,914
Foreign currency forward contracts | Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	11,564
Foreign currency forward contracts | Designated as Hedging Instrument | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	951	1,895
Foreign currency forward contracts | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	1,000
Foreign currency forward contracts | Designated as Hedging Instrument | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	338	31,775
Foreign currency forward contracts | Not Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	4,440	5,414
Foreign currency forward contracts | Not Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	11,475	11,987
Fuel contracts | Designated as Hedging Instrument | Swaps | Other Assets
Asset Derivatives
Asset Derivatives	8,585	26,258
Fuel contracts | Designated as Hedging Instrument | Swaps | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	48,624	82,747
Fuel contracts | Designated as Hedging Instrument | Swaps | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	6,369	29,213
Fuel contracts | Designated as Hedging Instrument | Swaps | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	1,761
Fuel contracts | Not Designated as Hedging Instrument | Swaps | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	475
Fuel contracts | Not Designated as Hedging Instrument | Options | Other Assets
Asset Derivatives
Asset Derivatives		16,371
Fuel contracts | Not Designated as Hedging Instrument | Options | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	8,252
Fuel contracts | Not Designated as Hedging Instrument | Options | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	$ 8,230